Shelly: Methyl eugenol consumption by Bactrocera dorsalis 201 CONSUMPTION OF METHYL EUGENOL BY MALE BACTROCERA DORSALIS (DIPTERA: TEPHRITIDAE): LOW INCIDENCE OF REPEAT FEEDING TODD E. SHELLY Hawaiian Evolutionary Biology Program University of Hawaii Honolulu, HI 96822 ABSTRACT The tendency of male Bactrocera dorsalis (Hendel) to re-visit a methyl eugenol source following initial exposure was examined. The first field test investigated the effect of duration of exposure on subsequent capture probability. “Treated” males were allowed to feed on methyl eugenol for 30 s or had access to methyl eugenol for 1 h, 4 h, or 24 h immediately prior to release. Capture probabilities (1%-4%) did not differ significantly among the different treatments but were significantly below that (22%) recorded for “control” (unexposed) males. In a second field test, treated males were released 7 d, 21 d, or 35 d after an initial exposure (2 h) to methyl eugenol. Cap- ture probabilities (11%-18%) did not differ significantly among the different treat- ments but were significantly below that (34%) recorded for control males. Laboratory tests yielded similar results as both the incidence and duration of re-feeding on me- thyl eugenol were uniformly low for males held 7 d, 21 d, or 35 d after their initial ex- posure. By exposing sterile males to the lure prior to release, it may be possible to combine programs of male annihilation and sterile insect release. The present find- ings also suggest that the effectiveness of male annihilation efforts may be reduced in areas where wild males have consumed sufficient amounts of methyl eugenol from natural sources. Key Words: Oriental fruit fly, parapheromone. RESUMEN Se estudió la tendencia de las visitas continuas del macho de Bactrocera dorsalis a una fuente de methyl eugenol. En el primer ensayo se investigó el efecto de el tiempo de exposición en la posibilidad de captura. Los machos tratados fueron ali- mentados con methyl eugenol por 30 segundos y tuvieron acceso a el methyl eugenol por 1, 4 o 24 horas imediatamente antes de la liberacion de los machos. No hubo diferencias significativas para la captura (1-4%) entre los diferentes tratamientos, pero hubo diferencias entre los machos que habian sido expuestos al eugenol com- paradas con los machos sin tratamiento (22%). En el segundo experimento, los ma- chos tratados por dos horas con methyl eugenol fueron liberados a los 7, 21 o 35 días después de tratamiento. No hubo diferencias de captura entre tratamientos, pero la captura fué menor (34%) que en el testigo. Los ensayos de laboratorio dieron resulta- dos simlares en cuanto a la incidencia y la duración de la re-alimentación con methyl eugenol y la captura fué baja para los machos expuestos por 7, 21 o 35 días. Al exponer los machos estériles a el atrayente antes de su liberación, puede ser posible el combinar programas de eliminación de machos y de liberación de machos estériles. Los resultados sugieren que la eficiencia de la eliminación de machos puede aumentar en aquellas areas en las cuales los machos salvajes han consumido can- tidades suficientes de methyl eugenol proveniente de fuentes naturales. ———————————— The males of several economically important tephritid species are strongly at- tracted to particular chemical compounds, termed “male lures” or “paraphero- mones”, that either occur naturally in plants or are (presumed) synthetic analogues This article is from Florida Entomologist Online, Vol. 77, No. 2 (1994). FEO is available from the Florida Center for Library Automation gopher (sally.fcla.ufl.edu) and is identical to Florida Entomologist (An International Journal for the Americas). FEO is prepared by E. O. Painter Printing Co., P.O. Box 877, DeLeon Springs, FL. 32130. This document was created with FrameMaker 4.0.2 202 Florida Entomologist 77(2) June, 1994 of plant-borne substances (Chambers 1977; Sivinski & Calkins 1986; Fletcher 1987). Several well-known examples include the attraction of male Mediterranean fruit flies, Ceratitis capitata (Wiedemann), to trimedlure, male melon flies, Bactrocera cu- curbitae (Coquillett), to cue-lure, and male Oriental fruit flies, B. dorsalis (Hendel), to methyl eugenol. Owing to their powerful attractancy, parapheromones play an im- portant role in current control programs of tephritid pests, both in detecting incipi- ent population outbreaks and eradicating already established populations via male annihilation (Chambers 1977). Despite the wide use of male lures in control efforts, relatively little attention has been given to explaining the underlying biological basis of this sex-specific, chemical attraction. In a recent study on the Oriental fruit fly, Shelly & Dewire (1993) found that “treated” males that fed on methyl eugenol achieved significantly more matings than “control” males deprived of methyl eugenol. Interestingly, treated males had a mating advantage even when they fed on methyl eugenol for only 30 s and were tested 35 d post-feeding. The present study investigates the tendency of B. dorsalis males to re-visit a me- thyl eugenol source following an initial exposure. Specifically, two field experiments and one laboratory experiment were conducted to examine whether the duration of the initial exposure and the time elapsed since the initial exposure affected the inci- dence and duration of re-feeding. Based on the results of mating trials (Shelly & Dewire 1993), I predicted that neither the duration of the initial exposure (at least for exposure periods exceeding 30 s) nor the time elapsed since the initial feeding (at least for intervals up to 35 d) would significantly affect the tendency for re-feeding. MATERIALS AND METHODS Field Experiments All flies used in field tests were from a colony maintained by the USDA/ARS Trop- ical Fruit and Vegetable Laboratory, Honolulu, for approximately 70 generations (M. Fujimoto, pers. comm.) using standard rearing procedures (Tanaka et al. 1969). Non- irradiated pupae were obtained 2 d prior to eclosion, and adults were sexed within 5 d of eclosion [(sexual maturity in this stock is attained at about 10 d of age, (M. Fujimoto, pers. comm.)]. Males were kept in 5-liter plastic buckets (50 per bucket) covered with screen mesh and given food and water ad libitum. Experiments were conducted at 2 locations on the island of Oahu, Hawaii. Dur- ing September-October, 1991, I used a 0.6-ha citrus grove in the University of Hawaii Agricultural Experiment Station, Waimanalo, that contained approximately 60 or- ange trees (Citrus sinensis (L.)). The grove was bordered on two sides by an open field containing small patches of guava (Psidium guajava L.) and coffee (Coffea arabica L.) and on the other two sides by highly disturbed, second-growth forest. During May-July, 1992, field-work was conducted at the Kanewai Garden near the campus of the University of Hawaii, Honolulu. This small area (0.4 ha) contained six large mango trees (Mangifera indica L.) and was bordered by an open lot on one side and lawns containing non-host vegetation on the remaining sides. Two field experiments were performed. At Waimanalo, I examined whether the duration of exposure to methyl eugenol affected capture probability. As described be- low, treated males fed on methyl eugenol for only 30 s or had access to methyl eu- genol for 1 h, 4 h, or 24 h immediately prior to release. At the Kanewai Garden, I examined the effect of time lapse following initial feeding on capture probability. Treated males had access to methyl eugenol for 2 h and were released 7 d, 21 d, or 35 d later. An additional set of treated males was permitted to feed on methyl eugenol for only 30 s and was released 35 d later. Control males that had no exposure to me- thyl eugenol were also released in both experiments. Shelly: Methyl eugenol consumption by Bactrocera dorsalis 203 To obtain treated males, 1.5 ml of methyl eugenol was applied to 5-cm long cotton wicks, and the wicks, held upright in small plastic containers, were placed singly in the appropriate buckets during midday. Buckets were placed on a shaded outdoor porch where air temperatures varied between 29-31 oC (or 23-31 oC during 24 h ex- posure periods). The feeding activity of individual males was not monitored during exposure periods of 1 h or more. To obtain males with 30 s feeding times, groups of 5- 10 males were observed in screen cages (30 cm cubes with a cloth sleeve on one side) containing a single wick. Individuals were removed after 30 s of feeding by gently “coaxing” them into a vial. In all cases, treated males were exposed to methyl eugenol at 14 d of age and correspondingly were released at the age of 14 d at the Waimanalo site and 21 d, 35 d, or 49 d at Kanewai Garden. At Waimanalo, control males were 14 d old at release, while at Kanewai Garden separate control groups of males aged 21 d, 35 d, and 49 d, respectively, were used for the two treatment categories. Prior to re- lease, control males and the males in the different treatment groups were cooled and marked on the thorax with different color combinations of enamel paint (a given combination was used only once at either field site). The cooling and painting proce- dures had no apparent adverse effects on male behavior, and individuals resumed “normal” activities within minutes of handling. The following protocol was used for the tests conducted at Waimanalo. On the day prior to a release, Steiner traps were placed singly in 16 different trees located throughout the grove. The same trees were used in all tests. Traps were suspended in the canopy by a 30-cm long wire fastened to a branch. Each trap contained a 5-cm long cotton wick to which 1.5 ml of methyl eugenol (3% naled) had been applied.